The present invention relates to a monofilament tape, which may be used as a dental floss. The floss is easy to slide between the teeth, effective at cleaning, gentle to the gums, and capable of carrying more flavor than comparable flosses.
The use of dental floss is recommended by virtually all dental health practitioners. Dental flossing has been shown to be effective in removing interdental plaque according to the Council on Dental Therapeutics. Despite these facts, only about 12% of the United States population use floss regularly. Of those who do use floss, consumers prefer flosses which are shred and fray resistant, pass easily between tight teeth, are gentle to the gums, refreshen the mouth, clean effectively, and are easy to use. Mouth freshening is controlled through the use of coatings, which typically comprise flavors, mouth fresheners, cleaning agents, polishing agents and the like. The more coating the floss substrate can carry, the better the floss may be at mouth freshening and cleaning.
Monofilament flosses made from poly(tetrafluoroethylene)/(xe2x80x9cPTFExe2x80x9d) provide most of the attributes discussed above, except for the ability to carry more flavor and other additives, and ease of handling. Many consumers feel that PTFE monofilament floss does not clean as well as conventional multi-filament flosses. In addition, the cost of PTFE floss is relatively high, mainly due to the high resin cost. Therefore, there is a need to replace PTFE with lower cost materials that will provide the above-mentioned consumer preferred attributes.
One technology that may be useful for dental floss applications is bicomponent fiber technology. Bicomponent fibers are fibers which are made from two different polymers. Bicomponent fibers are also known as xe2x80x9cconjugatexe2x80x9d, xe2x80x9ccompositexe2x80x9d or xe2x80x9cheteroxe2x80x9d fibers. The main advantage of using this technology is to combine polymers with different properties in a single filament. Bicomponent fibers are commonly classified by their cross-sectional structures such as core-sheath; side-by-side; islands-in-the-sea; and pie-shaped.
U.S. Pat. No. 5,845,652 discloses the preparation of core-sheath bicomponent fibers using different materials and yarn constructions. The sheath polymers are thermoplastic elastomers, such as Pebax(copyright) and Hytrel(copyright) Brand polymers, and the core polymer is nylon. The specific examples set forth in the patent are based on 70/30 core-sheath fibers made from nylon/Pebax(copyright) 2533; nylon/Hytrel(copyright) 3078 and nylon/nylon having e.g., 144 filaments; a denier ranging from 580-730; no twist and tensile strengths of 3.4-5 g/d. These fibers were flattened on heated godets to bond the sheaths of the filaments during the fiber spinning process. The patent discloses the aspects of forming bulkable floss by utilizing different materials, mainly by using side-by-side bicomponent fibers. It also teaches methods of obtaining self-bulking and tension-induced bulkable floss.
U.S. Pat. No. 5,904,152 discloses a multifilament floss which has multiple cores made from nylon with either a Hytrel(copyright) or Pebax(copyright) Brand thermoplastic elastomeric polymer as the sheath.
U.S. Pat. No. 5,875,797 discloses a multicomponent, co-extruded, monofilament dental floss comprising a core comprising a first material such as nylon. The core is embedded in a sheath comprising a second material such as a thermoplastic elastomeric polymer. The floss has a continuous outer surface. The monofilament floss is prepared by using core-sheath technology and a die assembly during the co-extrusion process. Typical flosses disclosed in this patent have a denier of 600-700 and comprise 34 filaments with a 70/30 ratio of core polymer/sheath polymer. The disclosed flosses have a tenacity of 3-4.5 g/d and an elongation of at least 300%.
Despite the disclosure of the references, there is a continuing need for a floss which is shred and fray resistant, gentle to the gums, mouth freshening, effective at cleaning, easy to use, and passes readily between tight teeth.
The present invention provides an article comprising a bicomponent monofilament tape, said bicomponent monofilament tape comprising at least about 60 individual core fibers comprising a first polymer, said individual core fibers being embedded in and substantially completely surrounded by a fused sheath comprising a second polymer.
In another aspect, the present invention provides a process which includes the steps of providing at least about 60 bicomponent core-sheath fibers and fusing the sheaths to form a monofilament tape.
The bicomponent monofilament tape of the invention is made from the fusion of the sheaths of bicomponent core-sheath fibers. The bicomponent core-sheath fibers may be made by any process known in the art, including, but not limited to, using a co-extrusion melt spinning or solution spinning process. Co-extrusion of bicomponent fibers can be defined as extruding two polymers through the same spinneret with both polymers contained within the same filament with a distinct boundary between them.
FIG. 1 is a schematic illustration of a suitable process for making bicomponent fibers. The polymers utilized to form the core and the sheath are placed in single screw extruders (1A) and (1B). The polymers are heated and melted in the extruders, then passed through a spinneret (2) to form a plurality of co-extruded bicomponent fibers (3). The co-extruded bicomponent fibers are drawn by at least one roller (4). The co-extruded bicomponent fibers (3) are cooled in the region between the spinneret and the roller (4). The cooling may be provided by means known in the art, such as, but not limited, to chilled air (5). During the co-extrusion of the bicomponent fibers, the viscosities of the two polymers at the spinneret are preferably matched in order to prevent extrudate dogleg, which is the undesirable bending of the co-extruded bicomponent fiber (3) as it exits the spinneret (2). Matching of the viscosities may be achieved through the selection of polymeric components and the control of the temperature of the polymers in the single screw extruders (1A) and (1B) and the spinneret (2).
A spin finish may be applied by a roller (6) disposed in the cooling region (5) between the spinneret (2) and the first roller (4). Suitable spin finishes include, but are not limited to, Fasavin(copyright)2830 and Fasavin(copyright) 2758, which are commercially available through Zschimmer and Schwarz.
Roller (4) draws the plurality of bicomponent fibers exiting spinneret (2), i.e. the fibers are drawn, or stretched, as they pass through cooling zone (5) toward first roller (4). The effect of this drawing or stretching step is two-fold: first the fibers are reduced in diameter (i.e., their denier is reduced) and secondly, their tensile strength is increased. As is well known, the term xe2x80x9cdenierxe2x80x9d refers to the weight in grams per 9000 meters of fiber.
For example, at a constant rate of extrusion of polymer melt from spinneret (2), the fiber denier is reduced by increasing the rate of rotation of roller (4). Roller (4) typically rotates at a rate of from about 100 meters per minute to about 2000 meters per minute, preferably from about 400 meters per minute to about 1000 meters per minute. Preferably, a second roller (7) is used in conjunction with the first roller (4). The second roller (7) rotates at substantially the same speed as first roller (4). As can be seen by reference to FIG. 1 and FIG. 1A, the plurality of bicomponent fibers (3) are collated as they leave the lower region of the cooling zone and then come into contact with the lower surface of roller (4). The collated bicomponent fibers (3A) leave roller (4) and then come into contact with the lowermost surface (as seen in FIG. 1) of roller (7). The fibers continue to pass around roller (7) in a counterclockwise direction until they reach the uppermost surface (as seen in FIG. 1) of roller (7). The fibers are then conducted across the gap between rollers (4) and (7) and are brought into contact with the uppermost surface (as seen in FIG. 1) of roller (4). One wrap of the collated fibers is completed as the collated bundle of co-extruded fibers again reaches the point at which it first contacted roller (4) as it initially left cooling zone (5). After the completion of four such wraps around rollers (4) and (7), the collated fiber bundle (3A) leaves the lower surface (as seen in FIG. 1) of roller (7) and proceeds toward roller (8).
Roller (8) is set to rotate at a faster speed than that of roller (4) and (7), as a result of which the co-extruded bicomponent fibers (3) in the collated bundle (3A) are further drawn, i.e., as is well know in the art, their denier is further reduced and their tensile strength is further increased. As can be seen in FIG. 1B, collated fiber bundle (3A) wraps several times around roller (8) after which it passes to roller (9). Fiber bundle (3A) wraps several times around roller (9) before proceeding to roller (10).
Rollers (8) and (9) typically rotate at a speed of 100 meters to 3000 meters per minute, preferably at a speed of 1500 meters to 2500 meters per minute. Roller (9) should be operated at at least the same speed as roller (8). If desired, roller (9) can be operated at a faster speed than roller 8, in which case the denier of the fibers will be further reduced and their tensile strength further increased.
As mentioned, collated fiber bundle (3A) passes to roller (10) after leaving roller (9). Roller (10) is rotated at a speed which is lower than that of roller (9), as a result of which the fibers are allowed to relax. The fiber bundle (3A) passes several times around roller (10) and then passes under idle roller (11). The fiber bundle (3A) is then taken up on roller (12) to await further processing.
As is known in the art, any of the rollers (4), (7), (8), (9), and (10) may be heated. The temperatures of the heated rollers (4), (7), (8), (9), and (10) may range from about 30xc2x0 C. to about 80xc2x0 C., preferably from about 50xc2x0 C. to about 75xc2x0 C.
The bicomponent fibers utilized in the present invention are core-sheath fibers. The bicomponent fibers utilized in this invention may have cross-sectional shapes such as round; trilobal; cross; and others known in the art.
In order to be suitable for use in the present invention, the melting point of the polymer constituting the sheath component of the core-sheath bicomponent fibers must be lower than the melting point of the polymer constituting the core component. Suitable polymers for the core include polyamides such as, but not limited to, nylon 6, nylon 11, nylon 12, and nylon 66; polyesters such as, but not limited to, poly(ethylene terephthalate) (xe2x80x9cPETxe2x80x9d) and poly(butylene terephthalate) (xe2x80x9cPBTxe2x80x9d); polyolefins such as, but not limited to, polypropylene and polyethylene; and fluorinated polymers, such as, but not limited to, poly(vinylidene fluoride) and mixtures thereof. Nylon 6 and polypropylene are preferred.
Suitable polymers for the sheath include polyolefins such as, but not limited to, polyethylene (xe2x80x9cPExe2x80x9d) and polypropylene; polyesters such as, but not limited to, polycaprolactone (xe2x80x9cPCLxe2x80x9d); poly(ether-amides) such as, but not limited to, Pebax(copyright) 4033 SA and Pebax(copyright) 7233 SA (Trademark of Elf Atochem); poly(ether-esters) such as, but not limited to, Hytrel(copyright) 4056 (Trademark of DuPont) and Riteflex(copyright) poly(ether-ester) polymers available through Hoechst-Celanese; elastomers made from polyolefins, for example Engage(copyright) elastomers available through DuPont Dow; poly(ether-urethane) such as, but not limited to, Estane(copyright) poly(ether-urethane) polymers available from BF Goodrich; poly(ester urethane) such as, but not limited to, Estane(copyright) available through BF Goodrich; Kraton(copyright) polymers such as, but not limited to poly(styrene-ethylene/butylene-styrene) available through Shell; and poly(vinylidene fluoride) copolymers, such as, but not limited to, KynarFlex(copyright) 2800, available through Elf Atochem. Pebax(copyright) 4033, polyethylene, and PCL are preferred.
The ratio of the two components of the core-sheath fibers may be varied. All ratios used herein are based on volume percents. The ratio may range from about 10 percent core and about 90 percent sheath to about 90 percent core and about 10 percent sheath, preferably from about 20 percent core and about 80 percent sheath to about 80 percent core and about 20 percent sheath, more preferably from about 30 percent core and about 70 percent sheath to about 70 percent core and about 30 percent sheath.
During the process for making the monofilament bicomponent tape of the present invention, the sheaths of the bicomponent fibers are fused. As used herein, the term xe2x80x9cfusedxe2x80x9d means that the bicomponent fibers comprising collated bundle (3A) are exposed to a sufficient temperature for a sufficient period of time so that the sheaths of the individual core-sheath filaments (3) are completely melted and flow together to form a substantially continuous matrix of sheath material. The time and temperature conditions under which the fusion process takes place are, as would be understood by one skilled in the art, a function of the melting point of the particular polymer comprising the sheath material of the individual core-sheath fibers. The temperature at which the fusion of the sheaths of the core-sheath fibers is conducted is lower than the melting point of the cores of the core-sheath bicomponent fibers. As a result, the bicomponent monofilament tape of the present invention comprises a plurality of individual core fibers of polymeric material embedded in and substantially completely surrounded by fused sheath material. Fusion can be achieved, for example, by preheating fiber bundle 3A and then calendaring the preheated bundle. Calendaring is the passage of the fibers between the nip of two heated rollers separated by a specific gap which is set to control the thickness and width of the tape. The flexibility of the finished monofilament bicomponent tape can be controlled by the selection of suitable materials for core and sheath, by the ratio of sheath material to core material, and by the number and denier of the core-sheath filament in fiber bundle 3A.
FIG. 2 is a schematic illustration of a process for converting co-extruded bicomponent fibers into the monofilament tape of the present invention. The co-extruded bicomponent fibers (3) prepared as described above are pulled by a take-up roller (20). The number of fibers (3) is at least about 60, typically from about 150 to about 500, preferably from about 200 to about 450, more preferably from about 300 to about 400. In the conversion process, the co-extruded bicomponent fibers (3) are pulled through the nip of heated rollers (21A) and (21B) by the roller (20), to thereby fuse the sheaths of the individual bicomponent fibers, thus forming a monofilament tape in accordance with the teachings of the present invention. The temperature of the rollers (21A) and (21B) may range from about 40xc2x0 C. to about 90xc2x0 C., preferably from about 40xc2x0 C. to about 85xc2x0 C.
Optionally, the fibers (3) may be pulled from the supply roll (12) (FIG. 2) over at least one heated roller (22A) prior to calendaring. In a preferred embodiment, the fibers (3) are pulled over a second heated roller (22B) prior to calendaring at rolls (21A/21B). The temperature of the heated rollers (22A) and (22B) may range from about 40xc2x0 C. to about 170xc2x0 C. The fibers (3) may then enter at least one oven (23A) prior to calendaring. In a preferred embodiment, the fibers enter a second oven (23B) prior to calendaring. The temperature of the ovens may range from about 110xc2x0 C. to about 180xc2x0 C., preferably from about 115xc2x0 C. to about 170xc2x0 C. The monofilament tape may be pulled over at least one roller (24) at ambient temperature to aid in cooling the tape.
The thickness of the monofilament tape may range from about 0.013 mm to about 0.15 mm, preferably from about 0.025 mm to about 0.07 mm.
The combination of the soft sheath polymer and the strength provided by the core fibers allows balancing the floss properties to provide the desired suppleness and gentleness to the gums. The sheath material can be selected such that it has high coefficient of friction and critical surface free energy so that the tape can be coated at higher amounts of wax and other additives to provide ease of handling and other desirable properties.
For dental floss applications, the monofilament tape is coated with a coating composition containing wax, flavor, and other additives to form a dental floss. The amount of wax, flavor, and other additives typically coated on fibers to make floss is known in the art. Typically, the coating composition is added at from 15 weight percent to 60 weight percent, based on the weight of the monofilament tape. Suitable flavors include, but are not limited to, natural and synthetic flavor oils, such as mint and cinnamon. The flavor oils may be used as is, or may be encapsulated or supported on a carrier such as starch or modified starch.
Other additives include, but are not limited to, sweeteners such as bulk sweeteners, including sorbital and mannitol, and intense sweeteners including aspartame and sodium saccharin, as taught by U.S. Pat. No. 6,080,481, hereby incorporated by reference for the disclosure relating to waxes and sweeteners; abrasives, such as silica; dentrifices, such as a fluoride or fluoride containing compound; chemotherapeutic agents; cleaners, such as peroxides; and whiteners. Examples of suitable additives are disclosed in U.S. Pat. No. 5,908,039, the disclosure of which is hereby incorporated by reference.
The following Examples are intended to demonstrate the monofilament tape and the process of the invention. The Examples should in no way be interpreted as limiting the scope of the invention.